with the new features, I have been crunching various PDF that I'd previously regarded as un-convertable.

good results except that with a couple of big, complex ones, although the epub looks good in calibre, SIGIL chokes when asked to open it. not sure yet exactly why ,but CPU goes to 100% , sigil stops responding.

I have not yet tried a PC reboot but I note that if I kill sigil processes & then give it an easy book to open it is still happy.

i want to do more tests before raising a bug report - see if I can be more specific....

update

seems to be caused by photo collection at end of PDF - I see no images in calibre epub viewer, just lots of lines
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and the epub takes ages to load into viewer